I know this is an old topic, but since Chris is one of my favorite characters:
1) My favorite is Chris' initial story line. I thought Briscoe really conveyed the inner torment and anguish of the character and several of the scenes with Amy were very sweet and organic. They really felt like a big brother/little sister.
2) I would have liked to see the Jennings acknowledged as Collinses and for Quentin and Chris to interact more. Even if not on screen, mention could have been made that the two spent some evenings talking. Which brings me to a rather radical thought. Had the show ended in present time, I would have wanted Chris to be cured, via Quentin. As controversial as it may be, I had the idea that Quentin, just as a full moon is rising, destroys his portrait and kills himself with a silver bullet. His sacrifice for his family permanently lifts the curse.
3) Leaving the actress out of it, I can't deny Sabrina was devoted to Chris, so she didn't bother me that much. After a point in the Leviathan era, she was really the only one helping him. It irked me that Julia tried to help Jeb through blood analysis, etc. and all she seemed to do for Chris was lock him in a padded cell at Windcliff. I did like Chris and Carolyn, though. I'm undecided, maybe someone else completely. Perhaps Chris kills Sabrina, which leads to Quentin's actions stated above.
4) I accept the car accident. It happens.
5) The show was already on the decline, but I think Briscoe could have added something to PT. I don't know how much his sudden departure changed the game plan down the line. I was sorry to see him go, but I don't think the show would have lasted longer or been markedly improved if he hadn't.